Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other impurities are burnt out of pig iron to produce steel. Since steel is difficult to manufacture due to its high melting point, normal fuels and furnaces were insufficient and the open hearth furnace was developed to overcome this difficulty. Compared to Bessemer steel, which it displaced, its main advantages were that it did not expose the steel to excessive nitrogen (which would cause the steel to become brittle), was easier to control, and it permitted the melting and refining of large amounts of scrap iron and steel.

The open hearth furnace was first developed by German-born engineer Carl Wilhelm Siemens. In 1865, the French engineer Pierre-Émile Martin took out a license from Siemens and first applied his regenerative furnace for making steel. Their process was known as the Siemens–Martin process, and the furnace as an "open-hearth" furnace. Most open hearth furnaces were closed by the early 1990s, not least because of their slow operation, being replaced by the basic oxygen furnace or electric arc furnace.

While arguably the first primitive open hearth furnace was the Catalan forge, invented in Spain in the 8th century, it is usual to confine the term to certain 19th-century and later steelmaking processes, thus excluding bloomeries (including the Catalan forge), finery forges, and puddling furnaces from its application.

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The open hearth process is a batch process and a batch is called a "heat". The furnace is first inspected for possible damage. Once it is ready or repaired, it is charged with light scrap, such as sheet metal, shredded vehicles or waste metal. The furnace is heated using burning gas. Once it has melted, heavy scrap, such as building, construction or steel milling scrap is added, together with pig iron from blast furnaces. Once all the steel has melted, slag forming agents, such as limestone, are added. The oxygen in iron oxide and other impurities decarburize the pig iron by burning excess carbon away, forming steel. To increase the oxygen contents of the heat, iron ore can be added to the heat.

The process is far slower than that of Bessemer converter and thus easier to control and sample for quality assessment. Preparing a heat usually takes 8 h to 8 h 30 min to complete into steel. As the process is slow, it is not necessary to burn all the carbon away as in Bessemer process, but the process can be terminated at any given point when desired carbon contents has been achieved.

The furnace is tapped the same way a blast furnace is tapped; a hole is drilled on the side of the hearth and the raw steel flows out. Once all the steel has been tapped, the slag is skimmed away. The raw steel may be cast into ingots; this process is called teeming, or it may be used on continuous casting for the rolling mill.

The regenerators are the distinctive feature of the furnace and consist of fire-brick flues filled with bricks set on edge and arranged in such a way as to have a great number of small passages between them. The bricks absorb most of the heat from the outgoing waste gases and return it later to the incoming cold gases for combustion.

Sir Carl Wilhelm Siemens developed the Siemens regenerative furnace in the 1850s, and claimed in 1857 to be recovering enough heat to save 70–80% of the fuel. This furnace operates at a high temperature by using regenerative preheating of fuel and air for combustion. In regenerative preheating, the exhaust gases from the furnace are pumped into a chamber containing bricks, where heat is transferred from the gases to the bricks. The flow of the furnace is then reversed so that fuel and air pass through the chamber and are heated by the bricks. Through this method, an open-hearth furnace can reach temperatures high enough to melt steel, but Siemens did not initially use it for that.

In 1865, the French engineer Pierre-Émile Martin took out a license from Siemens and first applied his regenerative furnace for making steel. The most appealing characteristic of the Siemens regenerative furnace is the rapid production of large quantities of basic steel, used for example to construct high-rise buildings. The usual size of furnaces is 50 to 100 tons, but for some special processes they may have a capacity of 250 or even 500 tons.

The Siemens–Martin process complemented rather than replaced the Bessemer process. It is slower and thus easier to control. It also permits the melting and refining of large amounts of scrap steel, further lowering steel production costs and recycling an otherwise troublesome waste material. Its worst drawback is the fact that melting and refining a charge takes several hours. This was an advantage in the early 20th century, as it gave plant chemists time to analyze the steel and decide how much longer to refine it. But by about 1975, electronic instruments such as atomic absorption spectrophotometers had made analysis of the steel much easier and faster. The work environment around an open hearth furnace is said to be extremely dangerous, although that may be even more true of the environment around a basic oxygen or electric arc furnace.

Basic oxygen steelmaking eventually replaced the open hearth furnace. It rapidly superseded both the Bessemer process and Siemens–Martin process in Western Europe by the 1950s and in Eastern Europe by the 1980s. The open hearth steelmaking had superseded Bessemer process in UK by 1900, but elsewhere in Europe, especially in Germany, the Bessemer and Thomas processes were used until the late 1960s when they were superseded by basic oxygen steelmaking. The last open hearth furnace in the former East Germany was stopped in 1993. In the US, steel production using the Bessemer process ended in 1968 and the open hearth furnaces had stopped by 1992. In Hunedoara steel works, Romania the last 420-tonne capacity open hearth furnace was shut down on 12 June 1999, demolished and scrapped between 2001 and 2003, but the eight smokestacks of the furnaces remained until February 2011. The last open hearth shop in China was shut down in 2001. The nation with the highest share of steel produced with open hearth furnaces (almost 50%) is Ukraine.[1] The process is still in use in India and some parts of Ukraine. Russian retired its hearth furnace in March 2018, and considers preserving it as a museum artifact.[2]

1.
Furnace
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A furnace is a device used for high-temperature heating. The name derives from Greek word fornax, which means oven, the heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces. Furnace may also be a synonym for kiln, a used in the production of ceramics. Furnaces can be classified into four categories, based on efficiency. The first category would be natural draft, atmospheric burner furnaces and these furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through brick or masonry chimneys, air circulation depended on large, upwardly pitched pipes constructed of wood or metal The pipes would channel the warm air into floor or wall vents inside the home. This method of heating worked because warm air rises, the system was simple, had few controls, a single automatic gas valve, and no blower. These furnaces could be made to work with any fuel simply by adapting the burner area and they have been operated with wood, coke, coal, trash, paper, natural gas, and fuel oil. Furnaces that used solid fuels required daily maintenance to remove ash, in later years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home. The second category of furnace is the forced-air, atmospheric burner style with a cast-iron or sectional steel heat exchanger. Through the 1950s and 1960s, this style of furnace was used to replace the big, natural draft systems, the heated air was moved by blowers which were belt driven and designed for a wide range of speeds. These furnaces were still big and bulky compared to modern furnaces, energy efficiency would range anywhere from just over 50% to upward of 65% AFUE. This style furnace still used large, masonry or brick chimneys for flues and was designed to accommodate air-conditioning systems. The third category of furnace is the draft, mid-efficiency furnace with a steel heat exchanger. These furnaces were physically much more compact than the previous styles and they were equipped with combustion air blowers that would pull air through the heat exchanger which greatly increased fuel efficiency while allowing the heat exchangers to become smaller. These furnaces may have multi-speed blowers and were designed to work with central air-conditioning systems, the fourth category of furnace is the high-efficiency, or condensing furnace. High-efficiency furnaces can achieve from 89% to 98% fuel efficiency and this style of furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. Because the heat exchanger removes most of the heat from the exhaust gas, it actually condenses water vapor, the vent pipes are normally installed with PVC pipe versus metal vent pipe to prevent corrosion

2.
Steel
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Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties

3.
Melting point
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The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed

4.
Bessemer process
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The Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron, the oxidation also raises the temperature of the iron mass and keeps it molten. Related decarburizing with air processes had been used outside Europe for hundreds of years, one such process has existed since the 11th century in East Asia, where the scholar Shen Kuo describes its use in the Chinese iron and steel industry. In the 17th century, accounts by European travelers detailed its possible use by the Japanese, the modern process is named after its inventor, the Englishman Henry Bessemer, who took out a patent on the process in 1856. The process was said to be discovered in 1851 by the American inventor William Kelly. The process using a basic refractory lining is known as the basic Bessemer process or Gilchrist–Thomas process after the English discoverers Percy Gilchrist and these oxides either escape as gas or form a solid slag. The refractory lining of the converter also plays a role in the conversion — clay linings are used there is little phosphorus in the raw material - this is known as the acid Bessemer process. When the phosphorus content is high, dolomite, or sometimes magnesite and these are also known as Gilchrist-Thomas converters, after their inventor, Sidney Gilchrist Thomas. In order to produce steel with desired properties, additives such as spiegeleisen, when the required steel had been formed, it was poured into ladles and then transferred into moulds while the lighter slag was left behind. The conversion process, called the blow, was completed in approximately 20 minutes, during this period the progress of the oxidation of the impurities was judged by the appearance of the flame issuing from the mouth of the converter. The modern use of methods of recording the characteristics of the flame greatly aided the blower in controlling final product quality. After the blow, the metal was recarburized to the desired point and other alloying materials were added. A Bessemer converter could treat a heat of 5 to 30 tons at a time and they were usually operated in pairs, one being blown while another was being filled or tapped. Before the Bessemer process, Western Europe and the United States relied on the process to reduce the carbon content of white cast iron. It was possible to make low-quality puddled steel, but the process was difficult to control, high-quality steel was made by the reverse process of adding carbon to carbon-free wrought iron, usually imported from Sweden. The manufacturing process, called the process, consisted of heating bars of wrought iron together with charcoal for periods of up to a week in a long stone box. The blister steel was put in a crucible with wrought iron and melted, up to 3 tons of expensive coke was burnt for each ton of steel produced. Such steel when rolled into bars was sold at £50 to £60 a long ton, the most difficult and work-intensive part of the process, however, was the production of wrought iron done in finery forges in Sweden

5.
Germany
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Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of 357,021 square kilometres, with about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular destination in the world. Germanys capital and largest metropolis is Berlin, while its largest conurbation is the Ruhr, other major cities include Hamburg, Munich, Cologne, Frankfurt, Stuttgart, Düsseldorf and Leipzig. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity, a region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward, beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation, in 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic, the establishment of the national socialist dictatorship in 1933 led to World War II and the Holocaust. After a period of Allied occupation, two German states were founded, the Federal Republic of Germany and the German Democratic Republic, in 1990, the country was reunified. In the 21st century, Germany is a power and has the worlds fourth-largest economy by nominal GDP. As a global leader in industrial and technological sectors, it is both the worlds third-largest exporter and importer of goods. Germany is a country with a very high standard of living sustained by a skilled. It upholds a social security and universal health system, environmental protection. Germany was a member of the European Economic Community in 1957. It is part of the Schengen Area, and became a co-founder of the Eurozone in 1999, Germany is a member of the United Nations, NATO, the G8, the G20, and the OECD. The national military expenditure is the 9th highest in the world, the English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine. This in turn descends from Proto-Germanic *þiudiskaz popular, derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- people, the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a mine in Schöningen where three 380, 000-year-old wooden javelins were unearthed

6.
Electric arc furnace
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An electric arc furnace is a furnace that heats charged material by means of an electric arc. Industrial arc furnaces range in size from units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking. Arc furnaces used in laboratories and by dentists may have a capacity of only a few dozen grams. Industrial electric arc furnace temperatures can be up to 1,800 °C, Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc, and the current in the furnace terminals passes through the charged material. In the 19th century, a number of men had employed an arc to melt iron. The first electric arc furnaces were developed by Paul Héroult, of France, the Sanderson brothers formed The Sanderson Brothers steel Co. in Syracuse, New York, installing the first electric arc furnace in the U. S. This furnace is now on display at Station Square, Pittsburgh, initially electric steel was a specialty product for such uses as machine tools and spring steel. Arc furnaces were used to prepare calcium carbide for use in carbide lamps. The Stassano electric furnace is an arc type furnace that usually rotates to mix the bath, the Girod furnace is similar to the Héroult furnace. While EAFs were widely used in World War II for production of alloy steels, Steel, for low-cost, carbon steel long products in the U. S. market. In 1987, Nucor made the decision to expand into the flat products market, the roof also supports the refractory delta in its centre, through which one or more graphite electrodes enter. The hearth may be hemispherical in shape, or in an eccentric bottom tapping furnace, in modern meltshops, the furnace is often raised off the ground floor, so that ladles and slag pots can easily be manufactured under either end of the furnace. Separate from the structure is the electrode support and electrical system. Two configurations are possible, the supports and the roof tilt with the furnace. A typical alternating current furnace is powered by an electrical supply. Electrodes are round in section, and typically in segments with threaded couplings, so that as the electrodes wear, new segments can be added. The arc forms between the material and the electrode, the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc. The electric arc temperature reaches around 3000 °C, thus causing the lower sections of the electrodes glow incandescently when in operation, the electrodes are automatically raised and lowered by a positioning system, which may use either electric winch hoists or hydraulic cylinders

7.
Bloomery
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A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of capable of smelting iron. A bloomerys product is a mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, the bloomery has now largely been superseded by the blast furnace, which produces pig iron. A bloomery consists of a pit or chimney with heat-resistant walls made of earth, clay, near the bottom, one or more pipes enter through the side walls. These pipes, called tuyères, allow air to enter the furnace, either by natural draught, an opening at the bottom of the bloomery may be used to remove the bloom, or the bloomery can be tipped over and the bloom removed from the top. The first step taken before the bloomery can be used is the preparation of the charcoal, the charcoal is produced by heating wood to produce the nearly pure carbon fuel needed for the smelting process. The ore is broken into pieces and usually roasted in a fire to remove any moisture in the ore. Any large impurities in the ore can be crushed and removed, since slag from previous blooms may have a high iron content, it can also be broken up and recycled into the bloomery with the new ore. In operation, the bloomery is preheated by burning charcoal, and once hot, iron ore and additional charcoal are introduced through the top, as the desired product of a bloomery is iron which is easily forgeable, it requires a low carbon content. The temperature and ratio of charcoal to iron ore must be controlled to keep the iron from absorbing too much carbon. Cast iron occurs when the iron melts and absorbs 2% to 4% carbon, because the bloomery is self-fluxing the addition of limestone is not required to form a slag. The mixed iron and slag cool to form a spongy mass referred to as the bloom. Because the bloom is highly porous, and its spaces are full of slag. Iron treated this way is said to be wrought, and the resulting iron and it is also possible to produce blooms coated in steel by manipulating the charge of and air flow to the bloomery. The onset of the Iron Age in most parts of the world coincides with the first widespread use of the bloomery, while earlier examples of iron are found, their high nickel content indicates that this is meteoric iron. Other early samples of iron may have produced by accidental introduction of iron ore in bronze smelting operations. Iron appears to have been smelted in the West as early as 3000 BC, in the West, iron began to be used around 1200 BC

8.
Finery forge
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A finery forge is a hearth used to fine wrought iron, through the decarburization of the pig iron. The fining process involved liquifying cast iron in a fining hearth, Finery forges were used as early as 3rd century BC, based on archaeological evidence found at a site in Tieshengguo, China. The finery forge process was replaced by puddling process and the roller mill, in Europe, the concept of the finery forge may have been evident as early as the 13th century. The finery forge process began to be replaced in Europe from the late 18th century by others, of which puddling was the most successful, the new methods used mineral fuel, and freed the iron industry from its dependence on wood to make charcoal. There were several types of finery forges, the dominant type in Sweden was the German forge, which had a single hearth that was used for all processes. Its purity depended on the use of ore from the Dannemora mine, the Walloon forge was virtually the only kind used in Great Britain. The forge had two kinds of hearths, the finery to finish the product and the chafery to reheat the bloom that was the raw material of the process, in the finery, a workman known as the finer remelted pig iron so as to oxidise the carbon. This produced a lump of iron known as a bloom and this was consolidated using a water-powered hammer and returned to the finery. The next stages were undertaken by the hammerman, who in some iron-making areas such as South Yorkshire was also known as the stringsmith, in order to do this, he had to reheat the iron, for which he used the chafery. The fuel used in the finery had to be charcoal, as impurities in any mineral fuel would affect the quality of the iron, the waste product was allowed to cool in the hearth and removed as a mosser. In the Furness district they were left as the capstone of a wall, particularly near Spark Bridge. H. Schubert, History of British Iron and Steel Industry c.450 BC to AD1775, a. den Ouden, The Production of Wrought Iron in Finery Hearths, Historical Metallurgy 15, 63–87 and 16, 29–33. Hildebrand, Swedish Iron in the Seventeenth and Eighteenth Centuries, Export Industry Before Industrialization, P. King, The Cartel in Oregrounds Iron, Trading in the Raw Material for Steel During the 18th century, Journal of Industrial History 6, 25–48. Media related to Finery forges at Wikimedia Commons

9.
Blast furnace
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A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron, but also others such as lead or copper. The end products are usually molten metal and slag phases tapped from the bottom, the downward flow of the ore and flux in contact with an upflow of hot, carbon monoxide-rich combustion gases is a countercurrent exchange and chemical reaction process. In contrast, air furnaces are naturally aspirated, usually by the convection of hot gases in a chimney flue, according to this broad definition, bloomeries for iron, blowing houses for tin, and smelt mills for lead would be classified as blast furnaces. Blast furnaces existed in China from about 1st century AD and in the West from the High Middle Ages and they spread from the region around Namur in Wallonia in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal, the successful substitution of coke for charcoal is widely attributed to Abraham Darby in 1709. The efficiency of the process was enhanced by the practice of preheating the combustion air. The oldest extant blast furnaces were built during the Han Dynasty of China in the 1st century AD. However, cast iron tools and weapons were widespread in China by the 5th century BC. These early furnaces had clay walls and used phosphorus-containing minerals as a flux, the effectiveness of the Chinese blast furnace was enhanced during this period by the engineer Du Shi, who applied the power of waterwheels to piston-bellows in forging cast iron. He suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze, certainly, though, iron was essential to military success by the time the State of Qin had unified China. Usage of the blast and cupola furnace remained widespread during the Song and Tang Dynasties and this may have happened as early as the 4th century AD. The Chinese blast furnace remained in use well until the 20th century, the backyard furnaces favoured by Mao Zedong during the Great Leap Forward were of this type. In the regions with strong traditions of metallurgy, the production actually increased during this period. In most places in the other than in China, there is no evidence of the use of the blast furnace. Instead, iron was made by reduction in bloomeries. The bloomery process was invented probably in modern-day Xinjiang or other parts of Western China by Hans or Mongols around 800 BC. Iron finds in China proper are few before bloomeries were supplanted by the blast furnace in the 5th century BC which seems to have developed independently in the southern Chinese cultural sphere, in Europe, the Greeks, Celts, Romans, and Carthaginians all used this process. Several examples have found in France, and materials found in Tunisia suggest they were used there as well as in Antioch during the Hellenistic Period

10.
Combustion
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Combustion in a fire produces a flame, and the heat produced can make combustion self-sustaining. Combustion is often a sequence of elementary radical reactions. Solid fuels, such as wood, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the required to produce more of them. Combustion is often hot enough that light in the form of either glowing or a flame is produced, a simple example can be seen in the combustion of hydrogen and oxygen into water vapor, a reaction commonly used to fuel rocket engines. The bond energies in the play only a minor role, since they are similar to those in the combustion products. The heat of combustion is approximately -418 kJ per mole of O2 used up in the combustion reaction, uncatalyzed combustion in air requires fairly high temperatures. Complete combustion is stoichiometric with respect to the fuel, where there is no remaining fuel, thermodynamically, the chemical equilibrium of combustion in air is overwhelmingly on the side of the products. Thus, the smoke is usually toxic and contains unburned or partially oxidized products. Since combustion is rarely clean, flue gas cleaning or catalytic converters may be required by law, fires occur naturally, ignited by lightning strikes or by volcanic products. Combustion was the first controlled chemical reaction discovered by humans, in the form of campfires and bonfires, usually, the fuel is carbon, hydrocarbons or more complicated mixtures such as wood that contains partially oxidized hydrocarbons. Combustion is also currently the only used to power rockets. Combustion is also used to destroy waste, both nonhazardous and hazardous, oxidants for combustion have high oxidation potential and include atmospheric or pure oxygen, chlorine, fluorine, chlorine trifluoride, nitrous oxide and nitric acid. For instance, hydrogen burns in chlorine to form hydrogen chloride with the liberation of heat, although usually not catalyzed, combustion can be catalyzed by platinum or vanadium, as in the contact process. In complete combustion, the reactant burns in oxygen, producing a number of products. When a hydrocarbon burns in oxygen, the reaction will yield carbon dioxide. When elements are burned, the products are primarily the most common oxides, carbon will yield carbon dioxide, sulfur will yield sulfur dioxide, and iron will yield iron oxide. Nitrogen is not considered to be a combustible substance when oxygen is the oxidant, Combustion is not necessarily favorable to the maximum degree of oxidation, and it can be temperature-dependent. For example, sulfur trioxide is not produced quantitatively by the combustion of sulfur, NOx species appear in significant amounts above about 2,800 °F, and more is produced at higher temperatures

11.
East Germany
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East Germany, formally the German Democratic Republic, was an Eastern Bloc state during the Cold War period. The Soviet zone surrounded West Berlin, but did not include it, as a result, the German Democratic Republic was established in the Soviet Zone, while the Federal Republic was established in the three western zones. East Germany, which lies culturally in Central Germany, was a state of the Soviet Union. Soviet occupation authorities began transferring administrative responsibility to German communist leaders in 1948, Soviet forces, however, remained in the country throughout the Cold War. Until 1989, the GDR was governed by the Socialist Unity Party, though other parties participated in its alliance organisation. The economy was centrally planned, and increasingly state-owned, prices of basic goods and services were set by central government planners, rather than rising and falling through supply and demand. Although the GDR had to pay war reparations to the USSR. Nonetheless it did not match the growth of West Germany. Emigration to the West was a significant problem—as many of the emigrants were well-educated young people, the government fortified its western borders and, in 1961, built the Berlin Wall. Many people attempting to flee were killed by guards or booby traps. In 1989, numerous social and political forces in the GDR and abroad led to the fall of the Berlin Wall, the following year open elections were held, and international negotiations led to the signing of the Final Settlement treaty on the status and borders of Germany. The GDR was dissolved and Germany was unified on 3 October 1990, internally, the GDR also bordered the Soviet sector of Allied-occupied Berlin known as East Berlin which was also administered as the states de facto capital. It also bordered the three sectors occupied by the United States, United Kingdom and France known collectively as West Berlin. The three sectors occupied by the Western nations were sealed off from the rest of the GDR by the Berlin Wall from its construction in 1961 until it was brought down in 1989, the official name was Deutsche Demokratische Republik, usually abbreviated to DDR. West Germans, the media and statesmen purposely avoided the official name and its abbreviation, instead using terms like Ostzone, Sowjetische Besatzungszone. The centre of power in East Berlin was referred to as Pankow. Over time, however, the abbreviation DDR was also used colloquially by West Germans. However, this use was not always consistent, for example, before World War II, Ostdeutschland was used to describe all the territories east of the Elbe, as reflected in the works of sociologist Max Weber and political theorist Carl Schmitt

12.
Hunedoara steel works
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Building started in August 1882, with two blast furnaces 14.40 m high and 110 m3 in volume. The first three burned charcoal, while the last two ran on coke, iron ore was extracted from the mine near the Ghelari plant some 16 km away, and was brought there on a ropeway conveyor built at the same time as the first furnace. Increased production of cast iron had led to a demand for iron ore. Industrial-scale quarrying began at Ghelari in 1863, followed by mining from 1881. As the ropeway conveyor could no longer handle a significantly enlarged capacity, also in the same area were built the 18-km Govăjdia-Bătrâna River funicular for charcoal transport and the 14-km Govăjdia-Bunila one for bringing charcoal and limestone. The latter was supplied from local quarries and carried in by harnessed pack animals. The works were opened on June 12,1884. The following May, the second blast furnace went into operation, the factory administration moved there, and the old iron, forging and machine workshops gradually lost their importance, although the Govăjdia Blast Furnace remained active as late as 1918. In 1886, the practice of turning cast iron into steel began at Hunedoara, the cast iron was shipped to steel works at Cugir, Podbrezová and Diósgyőr, but the technical and economic results were unsatisfactory. Experiments within the Hunedoara works had failed due to deficiencies in the craftsmanship of the equipment. However, once they started operating again, a fire destroyed them, after which the 1887 cast iron moulding hall and the experimental Bessemer converter were rebuilt, operating for six months. A fourth furnace,288 m3 in volume and 3.3 m higher than the others, started production in August 1895, transylvania united with Romania in 1918, with the works passing into the ownership of the Romanian government the following year. Starting in 1926, engineers and economists insisted, through proposals they made and carried out, between 1937 and 1940, a modern steel production and rolling section was built, with machinery imported from Nazi Germany, covering 8500 m2 and fitted with four special components. First, the four Siemens-Martin open-hearth furnaces, heated by six gas generators, could each fit 25 loads of tons, with a total capacity of 90,000 tons of steel ingots per year. The alloy loaded into the furnaces was 75% cast iron and 25% scrap iron, second, the 5 ton-per-load electric furnace produced special steels for tools, including alloys of chromium and tungsten, up to 6000 tons a year. Later, this was modernized and moved to the foundry, third, the foundry room with pits for shaping steel into ingots. By 1957, Hunedoara had more than 36,000 residents and was coming to be seen as a factory town and they spurred the citys growth from 4800 residents in 1930 to almost 90,000 in 1990, making it the countrys largest city dependent on a single industry. Production reached its peak in 1982–84, stalling during the regimes last years, Hunedoara was the leading Romanian producer of long steel profiles, made in two electric arc furnaces

A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals and its alloys, …

Former blast furnace in Port of Sagunto, Valencia, Spain.

Blast furnace in Sestao, Spain. The furnace itself is inside the central girderwork.

Part of the gas cleaning system of a blast furnace in Monclova, Mexico. This one is about to be de-commissioned and replaced.

The left picture illustrates the fining process to make wrought iron from pig iron, with the right illustration displaying men working a blast furnace of smelting iron ore producing pig iron, from the Tiangong Kaiwu encyclopedia, 1637